title: Acclimation of nitrogen uptake capacity of rice to elevated atmospheric CO2 concentration.
abstract: OBJECTIVE
  Nitrogen (N) is a major factor affecting yield gain of crops under elevated atmospheric carbon dioxide concentrations [CO(2)]. It is well established that elevated [CO(2)] increases root mass, but there are inconsistent reports on the effects on N uptake capacity per root mass. In the present study, it was hypothesized that the responses of N uptake capacity would change with the duration of exposure to elevated [CO(2)].
  
  
  METHODS
  The hypothesis was tested by measuring N uptake capacity in rice plants exposed to long-term and short-term [CO(2)] treatments at different growth stages in plants grown under non-limiting N conditions in hydroponic culture. Seasonal changes in photosynthesis rate and transpiration rate were also measured.
  
  
  RESULTS
  In the long-term [CO(2)] study, leaf photosynthetic responses to intercellular CO(2) concentration (Ci) were not affected by elevated [CO(2)] before the heading stage, but the initial slope in this response was decreased by elevated [CO(2)] at the grain-filling stage. Nitrate and ammonium uptake capacities per root dry weight were not affected by elevated [CO(2)] at panicle initiation, but thereafter they were reduced by elevated [CO(2)] by 31-41 % at the full heading and mid-ripening growth stages. In the short-term study (24 h exposures), elevated [CO(2)] enhanced nitrate and ammonium uptake capacities at the early vegetative growth stage, but elevated [CO(2)] decreased the uptake capacities at the mid-reproductive stage.
  
  
  CONCLUSIONS
  This study showed that N uptake capacity was downregulated under long-term exposure to elevated [CO(2)] and its response to elevated [CO(2)] varied greatly with growth stage.
authors.affiliation: National Agricultural Research Center for Tohoku Region, Climate Change Laboratory, Shimokuriyagawa, Iwate, Japan. shimn@iwate-u.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Shimono
authors.forename: James A
authors.initials: JA
authors.lastname: Bunce
mesh_terms: D000064:Acclimatization; D001692:Biological Transport / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000187:drug effects* / Q000378:metabolism*; D010788:Photosynthesis / Q000187:drug effects; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018526:Plant Transpiration / Q000187:drug effects; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen